Precast Concrete

Recast reinforced concrete  articles such as column, fencing posts, door and  window frames, lintels, chajjas, copings,  cells, shelves, slabs, beams, louvers etc shall be of the grade or mix as indicated and cast in forms or  moulds. The forms shall be of timber or of  steel of  better  finish. Provision  shall be made in  the forms and moulds to accommodate fixing  devices  such as nibs, clips, hooks, bolts and Sonning of notches and holes. The units may  be precast on a cement or steel platform which should be  adequately oiled. This shall be  allowed only if the surface finish obtained is of  same standard as obtained  in the formwork. Each  unit shall be cast in one operation. 

Casting and Finish 

• You should ensure that concrete  shall be proportioned, mixed, placed. and thoroughly  compacted by vibration or  tamping to obtain a dense concrete which is  free  from voids and honey combings. 
• Precast concrete products  shall hue a dense  surface finish showing no course aggregates and shall have no cracks or  crevices which  may lead to disintegration of concrete or rusting of steel or interfere with the proper placing of units. 
• Ensure that all angles  of the precast units with the exception of the angles resulting  from the splayed or the chambered faces  shall be true right angles. The arises shall be clean and sharp except those which are specified or shown to be rounded. The wearing surface shall be true. Or being  fractured. the interior of the units shall present a clean and homogeneous appearance. Proper cover to reinforcement shall be ensured. 

Curing 

• After placing the concrete shall be adequately protected during setting and in the first stages of hardening from shocks and from harmful  effects of sunshine, drying winds and cold. The concrete shall  be cured for at least seven days. 
• The precast articles shall  be  matured for 28 days from the dates of casting before erection or being built in. Autoclaves can also be used to obtain required maturity of concrete. 

Marking and Storing 

• Precast articles shall be clearly marked to indicate the top of member and its location and orientation in the structure. While the concrete is green each unit shall be marked  with the date of casting. 
• Precast unit shall be stored, transported and placed  in position in such a manner that they will not be overstressed or damaged. For this purpose the position of lifting hooks shall be predetermined and lifting hooks provided during casting itself.